The present invention relates to a diaphragm-type pump.
In an engine of a spark-ignition type such as an internal combustion engine, high-pressure injection of fuel into cylinders is effective for improving fuel consumption and decreasing emission. As a high-pressure fuel pump for this purpose, there is a diaphragm-type pump which pressurizes fuel such as gasoline through an elastic diaphragm instead of pressurizing fuel, which is a fluid having a low viscosity, directly by a plunger.
In such a diaphragm-type pump, a plunger slidably provided in a cylinder is reciprocated by a driving means, e.g., a cam. As a result of reciprocation of the plunger, the diaphragm is deformed, and suction and discharge of fuel is performed.
In the pump with the above-described diaphragm, the diaphragm functions by repeating its deformation. Therefore, it is a subject of study to improve durability of the diaphragm. In order to improve the durability, it is necessary to restrict a degree of deformation of the diaphragm and also to effect deformation operation of the diaphragm regularly.
In the conventional diaphragm-type pump, however, when the rotational speed of the pump is increased or when the viscosity of lubricating oil is increased, deformation operation of the diaphragm becomes irregular. Consequently, the diaphragm is deformed to a degree beyond a predetermined maximum deformation degree, or is vibrated unnecessarily. If the diaphragm is brought into such a condition, although there will be no problem in relation to suction and discharge of fuel, fatigue failure of the diaphragm will be easily induced, thereby largely deteriorating the durability.